C. Warburton 339 
larvae, the larvae of the spinal canal, and those which first appear in the 
warble tumours. The smaller, spinous oesophageal larva has not yet been 
demonstrated for H. bovis, but in all the other instars Laake has indicated 
characters by which the two species may be differentiated. 
First-stage Larvae. 
The mouth armature and the spines on the terminal segment of the body 
serve to distinguish the two species in this stage. The differences are best 
indicated by diagrams. In the mouth-hooks, note in bovis the bifid anterior 
limb and the blunt posterior limb of the crescent, which is not closely applied 
to the median spur. In lineatum the hook is more crescentic with both limbs 
sharply pointed, and it touches the median spear tangentially. 
bovis lineatum 
The spines on the last segment of H. bovis are much larger than in 
H. lineatum, and it is particularly noticeable that in lineatum the two flattened 
spines flanking each spiracle are at least twice the size of the others, while 
in bovis they are not conspicuously larger. 
Antepenultimate (? third stage) Larva. 
At this stage the mouth-hooks, which can be observed in cleared specimens, 
present much the same differences as served to distinguish the species in instar 1. 
bovis lineatum 
In this ‘‘smooth" larva the middle segments are unarmed in both species, 
and there is nothing characteristic about the spiracles. 
Penultimate (? fourth stage) Larva. 
At this stage the species are best differentiated by the spiracles. Each 
spiracle is composed of a varying number of “discs" or rings. In II. bovis 
